A radio base station (RBS) of a communication network comprises antenna, radio frequency (RF) units for analogue to digital conversion of signals received at the antenna and for digital to analogue conversion of signals to be transmitted from the antenna, frequency conversion units, base band (BB) signal processing units etc. Historically, the RF units, frequency conversion units and BB signal processing units are placed physically together, but divided from the antenna. For a macro RBS, for example, the antenna may be placed on the roof of a building, for transmitted signals to be able to reach rather far away, and the rest of the RBS, e.g. RF units, frequency conversion units and BB signal processing units, may be placed in the basement. For leading analogue signals received at the antenna, and analogue signals to be transmitted from the antenna between the antenna and the rest of the RBS, rather expensive coaxial cables are needed. If, for example, cheaper twisted-pair wires are used, there is a risk that the signal will be degraded. This means that the distance between the antenna and the rest of the RBS cannot be especially long.
In more recent development, the RBS has been divided into a radio resource unit (RRU) and a base band unit (BBU), wherein the RRU comprises the RF units and the BBU comprises BB signal processing units. The RRU could be made rather small and is therefore placed together with the antenna. The BBU could be placed in a central station, such as in a basement of a building. Since signals between the RRU and the BBU can be sent digitally, transmission lines such as twisted-pair copper cables or optical fibers can be used, with techno-economic gains compared to heavy and expensive coaxial cables. This also means that there can be a longer distance between the RRU and the BBU, 10's of km, and therefore many BBUs can be placed together in fewer spots, with potential site simplifications for operators.
Especially, in dense urban areas, a larger amount of small cell RRUs need to be deployed as well as macro cell RRUs. An economically advantageous solution is then to concentrate the BBUs even more to hub sites. The hub sites then have a number of BBUs that can serve a larger number of RRUs. Normally one BBU serves more than one RRU. The concentration of BBUs in a hub site can vary, a hub site serving anything from a dozen to hundred of RRUs, or even thousands of RRUs, as suggested in the Chine Mobile concept of a centralized Radio Access Network (RAN) solution. In order to be able to connect such a large amount of RRUs to BBUs, and not the least, to achieve a scalable solution, i.e. such that it is possible to dynamically add or delete RRUs to the network, a distribution network is suggested between the RRUs and the BBUs. The distribution network may be an optical distribution network (ODN). For an architecture wherein RRUs are connected to BBUs via a distribution network, it is necessary to control connectivity of RRUs to BBUs, or connections between RRUs and BBUs.